A Measurement of the Down Quark Polarization Fraction in the Nucleon.

Dr. Tony Forest
Department of Physics, Nuclear and Electrical Engineering
Idaho State University

The contributions of a nucleon's constituents, quarks and gluons, to the spin of the nucleon has been a long standing question since the 1980s when it was first observed that quarks contribute less than 40%.
The spin physics program at ISU is working to measure the contribution of a nucleon's down quarks to its spin. This is referred to as the down quark fractional polarization. Measurements of this quantity when compared with the standard theoretical description of quark interactions, Quantum Chromodynamics, have yet to indicate a transition from the observed negative values to the predicted positive value of unity. One goal of ISU's spin physics program is to determine the veracity of the theoretical prediction through a series of measurements using the upgraded Cebaf Large Acceptance Spectrometer (CLAS).